This project will assess the nature of variation due to newly- arisen mutations in Drosophila, with respect to a number of several different life-history characteristics including age- specific female fecundity, age-specific male mating success, longevity, viability, and net fitness. Mutations will be accumulated on second chromosomes maintained free of selection. The aim is to test the theory that senescence is in part due to the accumulation of deleterious mutations with effects confined to late in life, by determining whether or not a significant fraction of mutational variation is age-specific in the way required by this theory. The nature of mutational variation will be compared with that maintained as standing variation, where earlier studies have suggested negative correlations between effects at different ages. Rates of mutation for genes controlling life-history characters will be estimated as part of this study.